Influence of river level fluctuations and climate on riverbank stability

Riverbank collapse is a natural part of the evolution of rivers. An unprecedented period of dry conditions and low flows between 2005 and 2010 led to more than 162 reported riverbank collapse-related incidents along the Lower River Murray, in South Australia (downstream of Lock 1 at Blanchetown to Wellington). On 4 February, 2009 a 60 × 20 m (70,000 m3) section of riverbank, near Long Island Marina, Murray Bridge, collapsed into the river, taking with it three unoccupied vehicles and several trees. This paper aims to: (i) model the Long Island Marina riverbank collapse incident in both 2D and 3D; (ii) examine the influence and sensitivity of river level fluctuations and climatic factors on riverbank stability; and (iii) determine the dominant triggers affecting collapse. The analysis has been undertaken using an integration of the limit equilibrium method, transient unsaturated flow modeling and digital elevation model and high resolution aerial images from a Geographic Information System. The paper demonstrates the efficacy of this framework and the accuracy of the predictions. It also reveals that river fluctuation, rather than climatic influences, dominates riverbank collapse in the Lower River Murray.